Studies are in progress which are designed to elucidate the molecular and cellular mechanisms which regulate hemopoietic cell differentiation in the human and experimental animal. Specific objectives include the study of regulatory defects in inherited disorders of hemopoietic development in man and studies on the effects of erythropoietin on cell differentiation in vitro. BIBLIOGRAPHIC REFERENCES: Kim, H.C., Marks, P. A., Rifkind, R. A., Maniatis, G. M., and Bank, A. Isolation and In Vitro Differentiation of Human Erythroid Precursor Cells. Blood, 47(5) :767-776, 1976. Reuben, R. C., Wife, R. L., Breslow, R., Rifkind R. A., and Marks, P.A. A New Group of Potent Inducers of Differentiation in Murine Erythroleukemia Cells. Proc. Nat'l Acad. Sci. U.S.A., 73(3): 862-866, 1976.